Method for leakage reduction in fabrication of high-density FRAM arrays

ABSTRACT

A method is provided for fabricating a ferroelectric capacitor structure including a method for etching and cleaning patterned ferroelectric capacitor structures in a semiconductor device. The method comprises etching portions of an upper electrode, etching ferroelectric material, and etching a lower electrode to define a patterned ferroelectric capacitor structure, and etching a portion of a lower electrode diffusion barrier structure. The method further comprises ashing the patterned ferroelectric capacitor structure using a first ashing process, where the ash comprises an oxygen/nitrogen/water-containing ash, performing a wet clean process after the first ashing process, and ashing the patterned ferroelectric capacitor structure using a second ashing process.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to Ser. No. 60/877,299 filed Dec. 27,2006, which is entitled “Method for Leakage Reduction in Fabrication ofHigh-Density FRAM Arrays” and is a continuation-in-part of Ser. No.11/016,400, now U.S. Pat. No. 7,220,600, Filed Dec. 17, 2004, which isentitled “Ferroelectric Capacitor Stack Etch and Cleaning Methods.”

FIELD OF INVENTION

The invention relates generally to semiconductor devices and moreparticularly to methods for cleaning etched ferroelectric capacitorstructures in the fabrication of semiconductor devices.

BACKGROUND OF THE INVENTION

Memory systems are used for storage of data, program code, and/or otherinformation in many electronic products, such as personal computersystems, embedded processor-based systems, video image processingcircuits, portable phones, and the like. Ferroelectric memory, sometimesreferred to as “FRAM” or “FERAM”, is a non-volatile form of memorycommonly organized in single-transistor, single-capacitor (1T1C) ortwo-transistor, two-capacitor (2T2C) cell configurations, in which eachmemory cell includes one or more pairs of access transistors and cellcapacitors formed using ferroelectric dielectric material. Thenon-volatility of an FERAM memory cell results from a bi-stable ormulti-stable characteristic of the ferroelectric dielectric material inthe cell capacitor(s), wherein the ferroelectric material has multipleelectrically distinguishable stable states. Ferroelectric memory isoften fabricated in stand-alone memory integrated circuits (ICs) and/orin other semiconductor products such as logic circuits having on-boardnon-volatile memory, microprocessors, DSPs, communications chips, etc.The ferroelectric memory cells are typically organized in an arrayarchitecture, such as folded-bitline, open-bitline, etc., wherein theindividual cells are selected by plateline and wordline signals fromaddress decoder circuitry, with the data being read from or written tothe cells along bitlines using latch or sense amp circuits. In a typical1T1C memory cell, a ferroelectric capacitor is coupled between aplateline signal and a source/drain of a MOS cell transistor, the othersource/drain is connected to a bitline, and the transistor gate isconnected to a wordline control signal to selectively couple thecapacitor with the bitline during read and write operations.

The ferroelectric memory arrays are typically constructed in a devicewafer along with CMOS logic circuits, wherein the cell transistors areformed concurrently with logic transistors in the device, and theferroelectric capacitors are constructed in a capacitor layer above thewafer substrate. For example, the construction of the ferroelectric cellcapacitors may be integrated into a CMOS fabrication process flow aftertransistor formation (e.g., after standard ‘front-end’ processing), andbefore the metalization or interconnection processing (e.g., before‘back-end’ processing). In a typical integration of ferroelectriccapacitors in a CMOS process flow, transistors are formed on/in asemiconductor body, and a pre-metal dielectric (PMD) layer isconstructed over the transistors, including tungsten contacts extendingthrough the PMD level dielectric to the gate and source/drain terminalsof the transistors. Ferroelectric cell capacitors are then constructedin a first inter-level or inter-layer dielectric layer (e.g., ILD0)above the PMD level, where one of the cell capacitor electrodes (e.g., alower or bottom electrode) is connected to a cell transistor terminal(e.g., typically a source/drain) through one of the tungsten PMDcontacts, wherein interconnection of the other capacitor electrode (thetop or upper electrode) and the remaining transistor terminals withother components (e.g., signal routing) is provided in one or moremetalization layers or levels above the ILD0 level.

In constructing the ferroelectric cell capacitors in the initial ILD0 orother level, it is important to minimize leakage between the upper andlower capacitor electrodes, as well as the crystallinity and orientationof the ferroelectric material that is formed over the lower electrode.However, conventional ferroelectric cell fabrication techniques oftenlead to unacceptable levels of leakage and degraded polarizationperformance of ferroelectric cell capacitors, particularly for scaledsmaller capacitor dimensions, whereby there is a need for improvedmethods for ferroelectric capacitor fabrication in the manufacture ofsemiconductor devices.

SUMMARY OF THE INVENTION

The invention is directed to a method of fabricating a ferroelectriccapacitor structure in a semiconductor device, the method comprisingforming a lower electrode diffusion barrier structure over a dielectricmaterial, the lower electrode at least partially engaging a conductivestructure in the dielectric material; forming a lower electrode over thelower electrode diffusion barrier structure; forming a ferroelectricmaterial over the lower electrode; forming an upper electrode over theferroelectric material; forming a patterned etch mask over the upperelectrode, the patterned etch mask exposing a portion of the upperelectrode; etching portions of the upper electrode, the ferroelectricmaterial, and the lower electrode to define a patterned ferroelectriccapacitor structure using the patterned etch mask; etching a portion ofthe lower electrode diffusion barrier structure using the patterned etchmask; ashing the patterned ferroelectric capacitor structure using afirst ashing process comprising an oxygen/nitrogen/water-containing ash;performing a wet clean process after the first ashing process; andashing the patterned ferroelectric capacitor structure using a secondashing process.

The following description and annexed drawings set forth in detailcertain illustrative aspects and implementations of the invention. Theseare indicative of but a few of the various ways in which the principlesof the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial side elevation view in section illustrating anexemplary ferroelectric memory cell in a portion of a semiconductordevice wafer in accordance with one or more aspects of the inventionhaving a ferroelectric cell capacitor with a lower electrode coupledwith a MOS cell transistor source/drain to form a 1T1C ferroelectricmemory cell;

FIG. 1B is a partial side elevation view in section further illustratingthe ferroelectric cell capacitor structure in the memory cell of FIG.1A;

FIG. 2 is a flow diagram illustrating a process for fabricatingsemiconductor devices with ferroelectric capacitors in which one or moreaspects of the invention may be carried out;

FIG. 3 is a flow diagram illustrating a first exemplary technique foretching and cleaning the ferroelectric capacitor stack in the device ofFIGS. 1A and 1B according to the invention;

FIGS. 4A-4T are partial side elevation views in section illustratingformation of a ferroelectric memory cell ferroelectric capacitor stackin the device of FIGS. 1A and 1B generally according to the fabricationprocess of FIG. 2 using the stack etching and cleaning techniques ofFIG. 3 in accordance with one or more aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the attacheddrawing figures, wherein like reference numerals are used to refer tolike elements throughout. The invention relates to the use ofwater-containing post stack etch (PSE) processes and wet-cleaning ofetched ferroelectric capacitor stack structures, by which capacitorleakage may be mitigated in the fabrication of semiconductor devices,for example, devices having memory cells with ferroelectric cellcapacitors or other devices, such as integrated circuits, in whichferroelectric capacitors are used. The various aspects and advantages ofthe invention are hereinafter illustrated and described in conjunctionwith the drawings, wherein the illustrated structures are notnecessarily drawn to scale.

FIGS. 1A and 1B illustrate an exemplary ferroelectric memory cell (1T1C)with a cell transistor T and a ferroelectric capacitor C in asemiconductor device 2 formed in a wafer comprising a silicon substrate4 in accordance with various aspects of the invention. Although theexemplary device 2 employs 1T1C cell structures that may be configuredin a folded bitline array, the various aspects of the invention are notlimited to any particular cell type or array architecture, and mayalternatively be employed with 2T2C cells or other cell types, whereinall such alternative implementations are contemplated as falling withinthe scope of the invention and the appended claims. As illustrated inFIG. 1A, the cell transistor T includes a gate structure 10 having agate dielectric between a conductive gate electrode and a channel regionof the substrate 4, with source/drains 6 formed on either side of thechannel in an active region located between STI isolation structures 8,and conductive silicide structures 7 formed on the transistorsource/drains 6 and the gate 10.

A pre-metal dielectric (PMD) 14 is provided above the substrate 4 tocover the cell transistor T, where any suitable dielectric material andthickness may be used for the PMD layer 14. A conductive storage nodecontact 16 a and a conductive bitline contact 16 b are formed throughthe PMD layer 14 using any suitable materials and dimensions (e.g.,tungsten (W), polysilicon, or other conductive material) to connect withthe silicide structures 7 of the cell transistor source/drains 6,wherein the conductive polysilicon electrode of the gate 10 forms amemory array wordline connection in the illustrated device 2. Thevertical ferroelectric capacitor C is formed above the cell storage nodesource/drain contact 16 a (e.g., above the PMD level), and comprises abilayer lower electrode diffusion barrier structure 30 a, 30 b, and abilayer lower or bottom electrode 18 a, 18 b with an overlyingferroelectric material 20 (PZT in this example), and a bilayer upper ortop electrode 22 above the PZT 20. A multilayer sidewall or upperdiffusion barrier 46 is formed over the patterned ferroelectriccapacitor C, including an aluminum oxide material AlO_(X) and a siliconnitride material SiN. A first inter-level or inter-layer dielectriclayer (ILD0) 24 is formed over the barrier 46, and conductive contacts26 are formed through the dielectric 24 (and through the barrier 46) tocouple with the upper capacitor electrode 22 (plateline) and with thebitline contact 16 in the PMD level 14, wherein the device 2 may includefurther overlying metalization layers or levels (not shown).

FIG. 1B illustrates further details of the exemplary ferroelectriccapacitor C, which comprises a PZT ferroelectric material 20 sandwichedin a vertical capacitor stack structure between a multilayer upper (top)electrode 22 a, 22 b (collectively referred to as 22) and a multilayerlower (bottom) electrode 18 a, 18 b (18 collectively), where a remnantportion of a capacitor stack etch hardmask 32 is situated between theupper electrode 22 and an ILD0 plateline contact 26. At least a portionof the lower electrode diffusion barrier 30 a, 30 b (30 collectively) isformed over the storage node contact 16 a in the PMD dielectric 14. Anysuitable single or multilayer upper and lower electrodes or diffusionbarriers may be employed within the scope of the invention. Theconductive diffusion barrier 30 is formed on the storage node contact 16a prior to deposition of the lower electrode layers 18 a and 18 b, forprotecting the PMD contact 16 a during subsequent processing of thecapacitor dielectric 20. The conductive barrier 30 can be any suitableconductive material or materials that prevent or inhibit degradation ofthe contact 16 a, such as TiAlN or other possible barriers (some ofwhich have a slow oxidation rate compared to TiN) which include: TaSiN,TiSiN, TiN, TaN, HfN, ZrN, HfAlN, CrN, TaAlN, CrAlN, or any otherconductive material, or stacks or combinations thereof, where thebarrier 30 a, 30 b (30 collectively) is preferably thin, such as havinga thickness of about 100 nm or less in one example. The exemplary lowerelectrode barrier 30 in the device 2 comprises a TiN first barrier layer30 a of any suitable thickness (e.g., about 40 nm in one example), and aTiAlN second barrier layer 30 b of any suitable thickness, such as about30 nm in the illustrated implementation. Alternatively, the secondbarrier layer 30 b could be TiAlON, or a single barrier layer 30 couldbe formed over all or a portion of the contact 16 a, such as TiAlNhaving a thickness of about 60 nm in one possible implementation.

The lower electrode layers 18 are formed on the barrier 30 so as to makeelectrical connection with the underlying contact 16 a. In one example,the lower electrode 18 has a total thickness of about 25-100 nm, isstable in oxygen, and comprises a noble metal or conductive oxide suchas Ir, IrO_(x), Pt, Pd, PdO_(x), Au, Ru, RuO_(x), Rh, RhO_(x), LaSrCoO₃,(Ba,Sr)RuO₃, LaNiO₃ or stacks or combinations thereof, although othermaterials may be used. In cases where PZT material is used for theferroelectric 20, suitable exemplary bottom electrodes 18 include either50 nm Ir or a stack comprised of 30 nm IrO_(x) and 20 nm Ir. In theexemplary device 2, a lower Iridium (Ir) layer 18 a is formed on thebarrier 30 b to any suitable thickness, such as about 20 nm in theillustrated example. A lower Iridium Oxide (IrO_(x)) layer 18 b is thenformed over the lower Ir layer 18 a to any suitable thickness, such asabout 30 nm in the illustrated implementation. The IrO_(x) layer 18 bmay advantageously operate to improve switching endurance fatigueproperties by curing oxygen vacancies in the overlying PZT material 20,wherein it is desirable to avoid or mitigate reduction of (e.g., loss ofoxygen content from) the IrO_(x) layer 18 b during formation of the PZT20.

The exemplary ferroelectric material 20 is PZT having any suitablethickness, such as about 300 to 1000 Å, preferably about 700 Å in oneexample, where the PZT may be formed by any suitable deposition methodor other material formation techniques, such as metal organic chemicalvapor deposition (MOCVD) in the device 2, preferably in a manner thatavoids or inhibits reduction of the IrO_(x) material 18 b. Optionalpost-deposition rapid thermal annealing (RTA) may be employed to providedesired material properties of the PZT capacitor dielectric 20. Anysuitable ferroelectric material 20 may be used, wherein the invention isnot limited to PZT.

The upper electrode 22 includes an upper IrO_(x) layer 22 a formed overthe PZT 20 to any suitable thickness, such as about 100 nm or less, aswell as an upper Ir layer 22 b formed over the upper IrO_(x) layer 22 ato any suitable thickness, such as about 100 nm or less. A hardmask 32is formed above the upper Ir layer 22 b, for use in etching thepatterned ferroelectric capacitor stack structure C, where the hardmask32 can be any suitable material such as TiN, TiAlN, etc. In combinationwith the PZT ferroelectric material 20, other materials may besubstituted for the upper IrO_(x) layer 22 a, wherein it is advantageousto have a conductive oxide top electrode such as IrO_(x), RuO_(x),RhO_(x), PdO_(x), PtO_(x), AgO_(x), (Ba,Sr)RuO₃, LaSrCoO₃, LaNiO₃,YBa₂Cu₃O_(7-x) rather than a single pure noble metal, so as to minimizedegradation due to many opposite state write/read operations (fatigue).Moreover, it is advantageous to have the upper Ir layer 22 b or anothersuitable noble metal layer above the upper oxide layer 22 a to providelow resistance for connection of the upper electrode structure to thesubsequently formed plateline contact 26 and the hardmask 32, althoughnot a strict requirement of the invention.

The conductive hardmask 32 is deposited over the upper electrode 22, andis then patterned using any suitable lithographic techniques.Thereafter, the patterned hard mask 32 is used in selectively etchingthe upper and lower electrodes and the PZT 20 to define a patternedvertical ferroelectric capacitor structure C as shown in FIG. 1B. Inaddition, the single mask 32 is used in the exemplary device 2 foretching the exposed lower electrode diffusion barrier bilayer structure30 a, 30 b, wherein the use of a single stack etch mask 32 facilitatesscaling the dimensions of the ferroelectric capacitor C in the device 2.The hardmask 32 may be any suitable single or multilayer material andneed not remain over the upper electrode following capacitor stackstructure patterning. In the exemplary device 2, a single layer TiN orTiAlN 32 is formed over the upper Ir layer 22 b, and is patterned andused as an etch mask while etching the ferroelectric capacitor structureC.

The device 2 further includes a single or multilayer upper or sidewalldiffusion barrier 46 formed over the patterned capacitor stack structureC, which operates to inhibit hydrogen diffusion into the PZT material 20during subsequent fabrication processing. In the exemplary device 2, thehydrogen barrier 46 includes an aluminum oxide (AlO_(x)) first layerformed over the patterned capacitor C, and a silicon nitride (SiN)second upper diffusion barrier layer formed over the AlO_(x). The ILD0material 24 is then formed over the upper barrier 46, and conductivecontacts 26 are formed through the ILD0 24 for connection to the upperelectrode of the capacitor C (e.g., plateline connection), where theplateline contact 26 may be coupled to the Ir layer 22 b through aportion of the remaining hardmask 32, as shown in FIG. 1B, or may bedirectly connected to the upper Ir 22 b.

Referring now to FIGS. 2-6I, FIGS. 2, 3, and 5 illustrate two exemplaryimplementations of an exemplary semiconductor device fabrication processflow or method 100 according to one or more aspects of the invention,and FIGS. 4A-4T and 6A-6I illustrate the exemplary device 2 undergoingprocessing at various stages of fabrication. While the method 100 ofFIGS. 2, 3, and 5 is illustrated and described below as a series of actsor events, it will be appreciated that the invention is not limited bythe illustrated ordering of such acts or events. For example, some actsmay occur in different orders and/or concurrently with other acts orevents apart from those illustrated and/or described herein, inaccordance with the invention. In addition, not all illustrated stepsmay be required to implement a methodology in accordance with theinvention.

While the method 100 of FIGS. 2, 3, and 5 is illustrated and describedbelow as a series of acts or events, it will be appreciated that theinvention is not limited by the illustrated ordering of such acts orevents. For example, some acts may occur in different orders and/orconcurrently with other acts or events apart from those illustratedand/or described herein, in accordance with the invention. In addition,not all illustrated steps may be required to implement a methodology inaccordance with the invention.

The methods of the invention, moreover, may be implemented inassociation with the fabrication of devices illustrated and describedherein as well as in association with other devices and structures notillustrated. For example, the exemplary method 100 may be employed infabricating the exemplary semiconductor device 2 above or otherferroelectric memory devices and ferroelectric capacitors thereof. Also,while the following examples illustrate exemplary ferroelectriccapacitors formed using PZT ferroelectric material and Ir/IrO_(x)electrode materials, the invention may be employed in association withferroelectric capacitors fabricated with any suitable dielectric andelectrode materials, wherein all such variant implementations arecontemplated as falling within the scope of the invention.

In addition, while the exemplary semiconductor devices are illustratedherein with ferroelectric capacitors C formed in a dielectric layer orlevel (ILD0 24 in FIGS. 1A and 1B) after front-end contact formation andprior to formation of overlying metalization levels, the various aspectsof the invention may be employed at other points in a fabricationprocess, for example, wherein the ferroelectric capacitors are formed atany level in a multi-level semiconductor device design. Furthermore, theinvention may be employed in semiconductor devices (e.g., integratedcircuits) fabricated on or in any type of semiconductor body, includingbut not limited to silicon substrates (e.g., such as the semiconductorbody 4 in the device 2 of FIGS. 1A, 1B, 4A-4T), SOI wafers, epitaxiallayers formed above a substrate, etc. In this regard, the invention isnot limited to the examples illustrated and described herein, whereinall such alternative implementations are contemplated as falling withinthe scope of the invention and the appended claims.

FIG. 2 illustrates the method 100 including capacitor stack etching andcleaning at 128, wherein one embodiment of the processing at 128 isfurther illustrated in FIG. 3. FIGS. 4A-4T, in turn, illustrate thedevice 2 being processed according to the embodiment of FIGS. 2 and 3,as described further below.

In FIG. 2, the method 100 begins at 102, wherein front-end processing isperformed at 104, such as creation of n and p-wells in the semiconductorbody 4 and isolation structures (e.g., shallow trench isolation (STI)structures 8 in FIG. 4A or field oxide structures formed using localoxidation of silicon (LOCOS) techniques) in field areas of the wafer. At106, transistors are formed for logic or analog circuitry and forferroelectric memory cells (e.g., the exemplary memory cell transistor Tis formed in the semiconductor body 4 in FIG. 4A). At 108, silicidestructures 7 are formed at the transistor terminals (e.g., source/drainsand gate), an initial dielectric material is formed over thetransistors, referred to herein as a pre-metal dielectric (PMD layer 14in FIG. 4A), and conductive contacts 16 (e.g., tungsten, polysilicon, orother conductive material) are formed through the PMD layer forconnection to the silicide 7 at the cell transistor bitline source/drain6 as well as the source/drain 6 for connection at a cell storage nodewith the subsequently formed ferroelectric cell capacitor. In theexemplary device 2, the gate 10 forms a wordline structure, whereincontacts 16 need not be formed directly over the individual transistorgates 10, as illustrated in FIG. 4A. Any suitable dielectric material 14of any desired thickness can be employed at 108 in forming the initialPMD layer 14. In one possible implementation, a selective etch process(reactive ion etching or other suitable etch process with appropriateetch mask, not shown) is used at 108 to selectively etch portions of thePMD material 14, thereby creating openings into which tungsten or otherconductive material 16 is provided to create the conductive contacts 16a and 16 b, as illustrated in FIG. 4A.

At 110-122, ferroelectric capacitor layers are formed over the PMD layer14 and the contacts 16 thereof (FIGS. 4B-4H), including formation ofupper and lower conductive capacitor electrode and diffusion barrierlayers 30, 18, 22, as well as a ferroelectric material (PZT) layer 20between the electrode layers 18 and 22. At 124 and 126, a conductivestack etch hardmask is then formed and patterned (FIGS. 4I and 4J). Ingeneral, any suitable materials, material thicknesses, and layerformation processes may be employed in forming the ferroelectriccapacitor dielectric, electrode, and barrier layers within the scope ofthe invention, including single or multilayers.

In the illustrated implementation, a bilayer conductive bottom or lowerelectrode diffusion barrier structure 30 is initially created at 110 and112 comprising a TiN layer 30 a formed at 110 over the PMD dielectric 14and the PMD tungsten contacts 16 (FIG. 4B) to a thickness of about 4 nmvia sputtering, chemical vapor deposition (CVD), or other suitablematerial deposition process 152, although other materials and processesmay be employed, including but not limited to TaSiN, TiSiN, TiN, TaN,HfN, ZrN, HfAlN, CrN, TaAlN, CrAlN, or any other conductive material 30formed to any suitable thickness. In the method 100, the depositionprocess 152 used for formation of the TiN layer 30 a is reactive sputterdeposition using Ar+N₂ or Ar+NH₃, although other inert gases can besubstituted instead of Ar for the process 152. Other suitable depositiontechniques 152 may include chemical vapor deposition (CVD) or plasmaenhanced CVD (PECVD). Referring also to FIG. 4C, when tungsten (W) isused for the contacts 16, it is preferred to deposit a bilayer diffusionbarrier 30 a and 30 b, as in the exemplary device 2. At 112 in FIG. 2, aTiAlN or TiAlON layer 30 b is deposited over the TiN layer 30 a via adeposition process 160, as illustrated in FIG. 4C. The layer 30 b may beformed to any suitable thickness at 112, such as about 30 nm in theillustrated implementation. Any suitable deposition process 160 may beemployed at 112, including but not limited to physical vapor deposition(PVD), CVD or PECVD deposition, wherein a preferred proportion ofaluminum in TiAlN is around 30-60% Al, more preferably about 40-50% inorder to have improved oxidation resistance.

The lower electrode layers 18 are then formed at 114 and 116. At 114, alower electrode metal layer 18 a is formed over the barrier 30 via adeposition process 162, as shown in FIG. 4D. In the exemplary device 2,the layer 18 a is Ir deposited by a sputter deposition process 162 to athickness of about 20 nm at a deposition temperature below 450 degreesC., although CVD or PVD processes and other materials and thicknessescould alternatively be employed at 114. Other suitable conductivematerials can be used for the layer 18 a, including but not limited toIrO_(x), Pt, Pd, PdO_(x), IrPt alloys, Au, Ru, RuO_(x), (Ba,Sr,Pb)RuO₃,(Sr,Ba,Pb)IrO₃, Rh, RhO_(x), LaSrCoO₃, etc., or any stack or combinationthereof. Thereafter at 116, a metal oxide layer 18 b is formed, such asa lower IrO_(x) deposited using a PVD or sputter deposition process 164to a thickness of about 30 nm in the exemplary device 2, as illustratedin FIG. 4E. In general, the upper and lower electrodes 18 and 22 in theillustrated device 2 are both bi-layers comprising iridium and iridiumoxide (Ir and IrO_(x)), with lead zirconate titanate (PZT) ferroelectricmaterial 20 formed between the IrO_(x) layers 18 b and 22 a of theelectrodes, wherein a first layer of Ir 18 a and an overlying IrO_(x)layer 18 b are used with the barrier layers 30 a and 30 b in theillustrated device 2, although the invention is not limited to anyparticular materials or thicknesses for these layers.

Referring also to FIG. 4F, a PZT ferroelectric material 20 is thenformed over the lower IrO_(x) layer 18 b at 118. The material 20 isdeposited at 118 over the lower electrode material 18 b using anyappropriate deposition process 172, such as metal organic chemical vapordeposition (MOCVD) using any suitable ferroelectric materials, includingbut not limited to Pb(Zr,Ti)O₃ (lead zirconate titanate, PZT), doped PZTwith donors (Nb, La, Ta) acceptors (Mn, Co, Fe, Ni, Al) and/or both, orPZT doped and alloyed with SrTiO₃, BaTiO₃ or CaTiO₃, or stacks orcombinations thereof, or other (e.g., non-PZT) ferroelectric materialformed to any desired thickness (e.g., 300 to 1000 Å, preferably about700 Å in the illustrated example).

Referring now to FIGS. 2 and 4G, after the deposition of the PZTmaterial 20, the top electrode 22 is formed at 120-122 using anysuitable conductive material or materials, such as Ir, IrO_(x), RuO_(x),RhO_(x), PdO_(x), PtO_(x), AgO_(x), (Ba, Sr)RuO₃, LaSrCoO₃, LaNiO₃,YBa₂Cu₃O_(7-x) with a noble metal layer thereover, or stacks orcombinations thereof. In the illustrated device 2, the upper electrode22 is a bi-layer comprising an upper IrO_(x) layer 22 a formed over thePZT 20, and an Ir layer 22 b formed over the IrO_(x) layer 22 a, whereinthe electrode layers 22 may be formed at 120 and 122 to any desiredthickness using any suitable processes in accordance with the invention.In the illustrated example, an upper IrO_(x) layer 22 a is formed at 120on top of the ferroelectric material 20 via a sputter deposition processor reactive PVD process 174 in Ar+O₂ (FIG. 4G) to a thickness of about100 nm or less (e.g., about 30 nm in one example). In thisimplementation, it is advantageous for Pb based ferroelectrics 20 tohave a conductive oxide top electrode such as IrO_(x), RuO_(x), RhO_(x),PdO_(x), PtO_(x), AgO_(x), (Ba,Sr)RuO₃, LaSrCoO₃, LaNiO₃, YBa₂Cu₃O_(7-x), rather than a pure noble metal directly over the PZT 20 tominimize degradation due to many opposite state write/read operations(fatigue). Moreover, where the first upper electrode material 22 a is anoxide, it is advantageous to have a noble metal layer 22 b above it tohelp maintain low contact resistance between the subsequently formedmetal plateline contact 26 and the oxide 22 a. Thus, in the exemplarymethod 100, an upper Ir layer 22 b or other suitable metal is depositedat 122, wherein the exemplary upper Ir layer 22 b is deposited to athickness of about 100 nm or less over the upper IrO_(x) 22 a in thedevice 2 using a deposition process 182, as shown in FIG. 4H. Anysuitable deposition process 182, conductive material 22 b, andthicknesses can be employed at 122, wherein the exemplary process 182 isa PVD deposition in Ar to form about 20 nm of Ir 22 b.

Referring also to FIG. 4I, a hard mask layer 32 is formed (e.g.,deposited over the upper Ir layer 22 b) at 124 of TiN, TiAlN, or othersuitable conductive material via a deposition process 183, where thehard mask 32 may be a single or multi-layer structure of any suitablethickness. As illustrated in FIG. 4J, the hardmask material 132 is thenpatterned so as to cover portions of the underlying layers 22, 20, 18,and 30 in a prospective capacitor region of the device 2, and the exposethe remainder of the device 2, so as to operate as a etch hard mask insubsequent capacitor stack structure etching. In this manner, the hardmask material 32 is pattered according to the desired final size (area)and shape of the capacitor C prior to performing the etch process at128.

At 128, the capacitor stack structure is defined by etching using thepatterned hard mask 32, wherein FIG. 3 illustrates one exemplaryimplementation of the etching and cleaning processing at 128 inaccordance with the invention. It has been found that performing a firstash operation wherein the first ash includes a water (H₂O)-containingash, followed by a wet clean operation, and a second ashing operation inan oxidizing atmosphere after the capacitor electrode and dielectriclayers have been patterned (e.g., etched), results in reduction inferroelectric capacitor leakage to the extent of about 2 to 3 orders ofmagnitude over prior art methods, wherein the etching and cleaningimplementation of FIGS. 3 and 4K-4Q performs these cleaning stepsfollowing the etching of the lower electrode diffusion barrier layers30.

Referring now to FIGS. 3 and 4K, the capacitor electrode andferroelectric material layers 22, 18, and 20 may be etched usingseparate etch processes and separate masks, or these may be etched usinga single process and a single mask 32 within the scope of the invention.In the exemplary device 2, a single etch mask 32 is employed at 140-143in FIG. 3 in conjunction with a reactive ion etching (RIE) process 184,that begins with removal of exposed portions of the upper electrodelayers 22 a and 22 b, as shown in FIG. 4K. At 141, the exposed portionof the ferroelectric material 20 is removed by the process 184 (FIG.4L). The process 184 continues at 142 to remove exposed portions of thelower electrode layers 18, thereby defining a patterned ferroelectriccapacitor structure C, as illustrated in FIG. 4M. In thisimplementation, the etch process 184 then continues at 143 to removeexposed portions of the lower electrode diffusion barrier layers 30, asshown in FIG. 4N, wherein the etch chemistry and settings of the etchprocess 184 may be adjusted between layers or separate etch processesmay be used. It is noted at this point that any suitable etch process orprocesses may be employed in patterning the capacitor structure layers,wherein the invention is not limited to reactive ion etching techniques.

Post-etch cleaning is then performed at 144-146. At 144, the patternedferroelectric capacitor structure C is ashed using a first ashingprocess 185 (FIG. 4O) in accordance with the invention. The first ashprocess 185 employs a plasma to remove residual particles caused by thecapacitor stack etch process 184 at a power of about 1400 W and apressure of about 2000 mT with an oxygen/nitrogen/water (O₂/N₂/H₂O) flowof about 3500/200/300 sccm, in one embodiment, and at a chucktemperature of about 300° C. In another embodiment, the O₂/N₂/H₂O flowwill be about 3500/200/400 sccm. Ash time will be from about 30 secondsto about 3 minutes, and in one embodiment, about 60 seconds.

At 145, a wet clean process 186 is performed (FIG. 4P) to further cleanthe stack structure C. In one embodiment, the wet clean operation 186 isperformed using 50% phosphoric acid at a temperature of about 65° C. forabout one minute. Further suitable cleaning fluids include, but are notlimited to, sulfuric acid and nitric acid. The wet clean operation 186is followed by a DI water rinse at 80° C.

A second ashing operation 188 is then performed (FIG. 4Q) at 146, withno intervening material formation steps between the wet clean process186 and the second ashing process 188 (e.g., the second ash is performedat 146 directly after the wet clean at 145). In the exemplary method100, the second ashing process 188 employs a plasma at an RF power ofabout 1500 W and a pressure of about 1000 mT for about 210 seconds withan oxygen (O₂) flow of about 4000 sccm (e.g., oxidizing ambient) and ata chuck temperature of about 325° C., although the invention is notlimited to these specific settings. An exemplary ash tool that may beused is the Fusion 200MC, although other tools may be employed and arecontemplated by the invention. The second ashing process 188 may beperformed using any suitable ashing tools or equipment, and may involveremote RF plasma (e.g., 13.5 MHz) and/or electron-cyclotron resonance(ECR) plasma ashing (e.g., 2 GHz) to facilitate provision of highcurrent, low energy plasma in the ashing operation 188.

Returning to FIG. 2 and also referring to FIG. 4R, an optional single ormultilayer hydrogen diffusion barrier 46 may then be formed at 130 (FIG.2) above the patterned ferroelectric capacitor C via suitable depositionprocess or processes 190 (FIG. 4R) to prevent or inhibit hydrogendiffusion into the ferroelectric material 20 in subsequent (e.g.,back-end) processing of the device 2. In one example, the barrier 46 hasa thickness of about 30 nm or less, and comprises a first layer ofAlO_(x), Ta₂O₅, AlN, TiO₂, ZrO₂, HfO₂, or any stack or combinationthereof, as well as a second barrier layer comprising SiN, AlN, orstacks or combinations thereof with a thickness of about 30 nm or less(e.g., AlO_(x) and SiN layers 46 in the device 2 of FIG. 1B above),where the barrier layers 46 can be formed by any suitable processing ormay alternatively be omitted in accordance with the invention. In theillustrated example, moreover, the AlO_(x) layer operates as a lead (Pb)and hydrogen (H) diffusion barrier while the silicon nitride (e.g.,Si₃N₄) layer is subsequently used as a contact etch stop. In thisexample, the AlO_(x) is deposited at 130 over the patternedferroelectric capacitor stack C using atomic layer deposition (ALD) 190,wherein other deposition techniques and materials may alternatively beused that do not react with the PZT material 20 of the patternedcapacitor structure C. The second hydrogen barrier layer is then formedat 130 by deposition of silicon nitride (Si₃N₄) over the AlO_(x) layerusing a PECVD or other suitable deposition process 190.

Following formation of the upper diffusion barrier 46 at 130, aninter-level dielectric (e.g., ILD0) is deposited at 132 (layer 24 inFIG. 4S), which is then selectively etched to form via/contact openingsfor electrical coupling to the upper ferroelectric capacitor electrode22 and to the previously formed bitline contact 16 b in the underlyinginitial PMD layer 14. The openings are then filled with conductivematerial (e.g., copper, aluminum, tungsten, or other conductivematerial) to form the bitline and capacitor plateline contacts or vias26 in the ILD0 layer (e.g., ILD0 vias (V0) in the capacitor level), asshown in FIG. 4S. The ILD material 24 may be silicon dioxide (SiO₂),FSG, or other suitable dielectric. Thereafter, further metalizationlevels can be formed at 134, as shown in FIG. 4T, including another ILDmaterial 80 (e.g., ILD1 level) with a conductive plateline routingstructure 82 and an ILD1 bitline via 84, as well as an overlying ILD2dielectric 90 in which a conductive (e.g., copper) bitline routingstructure 92 is formed, after which other back-end processing isperformed (not shown) to complete the device 2, and the exemplaryfabrication method 100 ends at 136.

In the above examples, the term “ash” is used to describe processes thatare highly oxidizing and can include other chemistries with or insteadof O₂. For example, the ash process may include chemistries such as N₂O,ozone, NO₂, instead of, or in addition to O₂, and also may include othercomponents such as noble gasses, including but not limited to Ar, Ne orHe. The process tool used in the invention may include an asher, butalternatively may be an etch tool. In particular, the alternatingoxidizing gasses have potential advantages over O₂ as the primaryoxidizing gasses since they are potentially more reactive. For example,these gases may create more O radicals that just O₂ after plasmaformation. In fact, if the desired process includes a significantsubstrate bias and operates at lower pressure, than a typical ash typetool may not have sufficient capability and in such instances a moreconventional etch tool may be utilized.

Although the invention has been illustrated and described with respectto one or more implementations, alterations and/or modifications may bemade to the illustrated examples without departing from the spirit andscope of the appended claims. In particular regard to the variousfunctions performed by the above described components or structures(assemblies, devices, circuits, systems, etc.), the terms (including areference to a “means”) used to describe such components are intended tocorrespond, unless otherwise indicated, to any component or structurewhich performs the specified function of the described component (e.g.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary implementations of the invention. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“including”, “includes”, “having”, “has”, “with”, or variants thereofare used in either the detailed description and the claims, such termsare intended to be inclusive in a manner similar to the term“comprising”.

1. A method comprising: forming a ferroelectric capacitor stack over asubstrate; forming a patterned etch mask over the ferroelectriccapacitor stack; etching at least a first portion of the ferroelectriccapacitor stack to form a patterned ferroelectric capacitor stack,wherein the first portion includes a layer having a noble metal; ashingthe patterned ferroelectric capacitor stack using at least oxygen,nitrogen, and water after the step of etching at least the first portionof the ferroelectric capacitor stack; performing a wet cleaning afterthe step of ashing the patterned ferroelectric capacitor stack using atleast oxygen, nitrogen, and water; ashing the patterned ferroelectriccapacitor stack at a temperate of at least 300° C. in an oxidizingambient after the step of performing the wet cleaning; and etching atleast a second portion of the ferroelectric capacitor stack after thestep of ashing the patterned ferroelectric capacitor stack at thetemperature of at least 300° C. in the oxidizing ambient.
 2. The methodof claim 1, wherein method further comprises forming a transistor atleast partially over the substrate prior to the step of forming theferroelectric capacitor stack.
 3. The method of claim 2, wherein thestep of forming further comprises: forming a first diffusion barrierover the substrate; forming a first electrode over the first diffusionbarrier; forming a ferroelectric layer over the first electrode; forminga second electrode over the ferroelectric layer, wherein the secondelectrode is the layer having the noble metal; and forming a seconddiffusion barrier over the second electrode.
 4. The method of claim 3,wherein the step of forming the first diffusion barrier over thesubstrate further comprises: forming a first diffusion barrier layerover the substrate; and forming a second diffusion barrier layer overthe first diffusion barrier layer.
 5. The method of claim 4, wherein thestep of forming the second diffusion barrier over the second electrodefurther comprises forming a third diffusion barrier layer over thesecond electrode.
 6. The method of claim 5, wherein the first diffusionbarrier layer is made of TiN, and wherein the second diffusion barrierlayer is made of TiAlIN or TiAlION, and wherein the third diffusionbather layer is made of TiAlIN or TiN.
 7. The method of claim 3, whereinthe step of forming the first electrode over the first diffusion barrierfurther comprises: forming a first electrode layer over the firstdiffusion barrier; and forming a second electrode layer of the firstelectrode layer.
 8. The method of claim 7, wherein the step of formingthe second electrode over the ferroelectric layer further comprises:forming a third electrode layer over the ferroelectric layer; andforming a fourth electrode layer of the third electrode layer.
 9. Themethod of claim 8, wherein the first and fourth electrode layers aremade of Ir, and wherein the second and third electrode layers are madeof IrO_(X).
 10. The method of claim 3, wherein the first portion of theferroelectric capacitor stack further comprises the ferroelectric layerover the first electrode, the second electrode, and a second diffusionbarrier.
 11. The method of claim 10, wherein the second portion of theferroelectric capacitor stack further comprises the first electrode andthe first diffusion barrier.
 12. The method of claim 1, wherein the stepof ashing the patterned ferroelectric capacitor stack using at leastoxygen, nitrogen, and water further comprises ashing the patternedferroelectric capacitor stack at a power of about 1400 W and a pressureof about 2000 mT.
 13. The method of claim 12, wherein the step of ashingthe patterned ferroelectric capacitor stack using at least oxygen,nitrogen, and water further comprises further comprises using a flow ofoxygen, nitrogen, and water of about 3500 sccm, about 200 sccm, andabout 400 sccm, respectively, at a temperature of about 300° C.
 14. Themethod of claim 3, wherein the ferroelectric layer is made of PZT.
 15. Amethod comprising: forming a transistor having a first source/drainregion and a second a first source/drain region forming in a substrate;forming a contact that is substantially in electrical contact with atleast one of the first source/drain region and the second source/drainregion; forming a ferroelectric capacitor stack by: forming a firstdiffusion barrier layer over at least a portion of the contact; forminga second diffusion barrier layer over the first diffusion barrier layer;forming a first electrode layer over the second diffusion barrier layer;forming a second electrode layer of the first electrode layer; forming aferroelectric layer over the second electrode layer; forming a thirdelectrode layer over the ferroelectric layer; forming a fourth electrodelayer of the third electrode layer, wherein the fourth electrode layerincludes a noble metal; and forming a third diffusion barrier layer overthe fourth electrode layer; forming a patterned etch mask over theferroelectric capacitor stack; etching at least the third diffusionbarrier layer, the third electrode layer, the fourth electrode layer,and the ferroelectric layer of the ferroelectric capacitor stack to forma patterned ferroelectric capacitor stack; ashing the patternedferroelectric capacitor stack using at least oxygen, nitrogen, and waterat a power of about 1400 W and a pressure of about 2000 mT after thestep of etching at least the third diffusion barrier layer, the thirdelectrode layer, the fourth electrode layer, and the ferroelectric layerof the ferroelectric capacitor stack; performing a wet cleaning afterthe step of ashing the patterned ferroelectric capacitor stack using atleast oxygen, nitrogen, and water; ashing the patterned ferroelectriccapacitor stack at a temperate of at least 300° C. in an oxidizingambient after the step of performing the wet cleaning; and etching atleast first diffusion barrier layer, the second diffusion barrier layer,the first electrode layer, and the second electrode layer of theferroelectric capacitor stack after the step of ashing the patternedferroelectric capacitor stack at the temperature of at least 300° C. inthe oxidizing ambient.
 16. The method of claim 15, wherein the firstdiffusion barrier layer is made of TiN, and wherein the second diffusionbarrier layer is made of TiAlIN or TiAlION, and wherein the thirddiffusion bather layer is made of TiAlIN or TiN.
 17. The method of claim15, wherein the first and fourth electrode layers are made of Ir, andwherein the second and third electrode layers are made of IrO_(X). 18.The method of claim 15, wherein the step of ashing the patternedferroelectric capacitor stack using at least oxygen, nitrogen, and waterfurther comprises further comprises using a flow of oxygen, nitrogen,and water of about 3500 sccm, about 200 sccm, and about 400 sccm,respectively, at a temperature of about 300° C.
 19. The method of claim15, wherein the ferroelectric layer is made of PZT.